The invention relates to a method for predicting defects of at least one electrolytic capacitor comprising:                measuring the ripple voltage between the contact terminals of the capacitor,        measuring the capacitor temperature,        determining (or measuring) the current flowing in the capacitor,        determining the value of an equivalent series resistance of the capacitor,        determining the value of a theoretical equivalent series resistance of said capacitor according to the temperature of the capacitor,        comparing the value of the equivalent series resistance of the capacitor with the theoretical series equivalent value of said capacitor, and        displaying at least one item of information representative of the state of ageing of the capacitor.        
The invention also relates to a converter converting a variable voltage into DC voltage comprising at least one power supply line, at least one electrolytic capacitor connected to an output of said converter, and a device for predicting defects.
The invention further relates to an uninterruptible power supply comprising a converter converting a variable voltage into DC voltage and an inverter.